Pneumatic tire

ABSTRACT

The present technology provides a pneumatic tire. In a tire meridian cross-sectional view, a profile line (PL 1 ) of a center land portion (X) defined by two center main grooves ( 14   a,    14   b ) protrudes outward in a tire radial direction further than a standard profile line (PL 0 ). Profile lines (PL 2,  PL 3 ) of sub-center land portions (Y 1,  Y 2 ) and shoulder land portions (Z 1,  Z 2 ) defined outward of the two center main grooves ( 14   a,    14   b ) in the tire width direction protrude outward in the tire radial direction further than the standard profile line (PL 0 ), the shoulder land portions (Z 1,  Z 2 ) being defined further outward than the sub-center land portions (Y 1,  Y 2 ). A pitch count (Po) of a vehicle mounting outer side region and a pitch count (Pi) of a vehicle mounting inner side region satisfy the relationship Po&lt;Pi.

TECHNICAL FIELD

The present technology relates to a pneumatic tire with steeringstability performance, anti-noise/vibration performance, and uneven wearresistance performance enhanced in a well-balanced manner.

BACKGROUND ART

To enhance steering stability performance, conventionally, the landportion width of a tread portion is made large so as to ensure treadrigidity. However, an excessively large land portion width results inreduced ground contact pressure at the center position in the tire widthdirection of the land portion. Accordingly, both end portions in thetire circumferential direction at approximately the center positiondeform inward toward the land portion. As a result, the footprint lengthis shortened causing contact with the ground and steering stabilityperformance to be degraded.

Technology relating to enhancement of steering stability performanceaccompanying enhanced contact with the ground is known (see JapaneseUnexamined Patent Application Publication No. 2002-029216A). In suchtechnology, straight-line stability performance, a kind of steeringstability performance, is enhanced by forming a land portion in a curvedshape protruding outward in the tire radial direction.

As described in Japanese Unexamined Patent Application Publication No.2002-029216A, by forming a land portion in a curved shape protrudingoutward in the tire radial direction, contact with the ground isenhanced. Note that the method of determining the curved shape describedin Japanese Unexamined Patent Application Publication No. 2002-029216Aemploys one type of road contact surface profile line extending over thewhole of the tread surface in the tire width direction.

In recent years, development of a pneumatic tire having superiorsteering stability performance as well as superior anti-noise/vibrationperformance and uneven wear resistance performance has been in demand.

SUMMARY

The present technology provides a pneumatic tire with steering stabilityperformance, anti-noise/vibration performance, and uneven wearresistance performance enhanced in a well-balanced manner.

A pneumatic tire of the present technology includes on either side of atire equatorial plane in a tire width direction, one center main grooveextending in a tire circumferential direction, one shoulder main grooveextending in the tire circumferential direction outward from the centermain groove in the tire width direction, and five land portionsextending in the tire circumferential direction, the land portions beingdefined by the four main grooves.

In a tire meridian cross-section of the pneumatic tire, a curved lineincluding at least two of four both end points of the two center maingrooves in the tire width direction is defined as a standard profileline. A profile line of a center land portion defined by the two centermain grooves protrudes outward in the tire radial direction further thanthe standard profile line. Profile lines of sub-center land portions andshoulder land portions defined outward of the two center main grooves inthe tire width direction protrude outward in the tire radial directionfurther than the standard profile line. The shoulder land portions aredefined further outward than the sub-center land portions. Further, theprofile lines of the sub-center land portions and the shoulder landportions each include an outermost point of the corresponding centermain groove in the tire width direction and both end points of thecorresponding shoulder main groove in the tire width direction, and arepresent on either side of the tire equatorial plane in the tire widthdirection. A pitch count Po of the vehicle mounting outer side regionand a pitch count Pi of the vehicle mounting inner side region satisfythe relationship Po<Pi.

In the pneumatic tire according to the present technology, the profilelines of the land portions defined in the tread portion, and the pitchcount of each vehicle mounting side region are enhanced. As a result, apneumatic tire according to the present technology can enhance steeringstability performance, anti-noise/vibration performance, and uneven wearresistance performance in a well-balanced manner.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a plan view of a tread surface of a pneumatic tire accordingto an embodiment of the present technology.

FIG. 2 is a tire meridian cross-sectional view of a tread portion of thepneumatic tire illustrated in FIG. 1.

FIGS. 3A and 3B are plan views illustrating ground contact patch formsof pneumatic tires. FIG. 3A illustrates a form of a conventionalpneumatic tire and FIG. 3B illustrates a form of the pneumatic tire ofthe present embodiment.

FIG. 4 is an enlarged view of the circled area B of FIG. 2.

DETAILED DESCRIPTION

The following is a detailed description of embodiments of a pneumatictire according to the present technology (hereinafter, referred to asthe Basic Embodiment and Additional Embodiments 1 to 3), based on thedrawings. Note that these embodiments are not intended to limit thepresent technology. The constituents of the embodiments includeconstituents that can be easily replaced by those skilled in the art andconstituents substantially the same as the constituents of theembodiments. In addition, the various embodiments included in theembodiments can be combined as desired within the scope of obviousnessby a person skilled in the art.

Basic Embodiment

A basic embodiment of the pneumatic tire according to the presenttechnology will now be described. In the following description, “tireradial direction” refers to a direction orthogonal to the axis ofrotation of a pneumatic tire; “inward in the tire radial direction”refers to a direction toward the axis of rotation in the tire radialdirection; and “outward in the tire radial direction” refers to adirection away from the axis of rotation in the tire radial direction.“Tire circumferential direction” refers to the circumferential directionwith the axis of rotation as the center axis. Furthermore, “tire widthdirection” refers to a direction parallel to the axis of rotation;“inward in the tire width direction” refers to a direction toward a tireequatorial plane (tire equatorial line) in the tire width direction; and“outward in the tire width direction” refers to a direction away fromthe tire equatorial plane in the tire width direction. Note that “tireequatorial plane” refers to a plane that is orthogonal to the axis ofrotation of the pneumatic tire and that passes through the center of thepneumatic tire along the width thereof.

FIG. 1 is a plan view of a tread surface of a pneumatic tire accordingto an embodiment of the present technology. Note that in FIG. 1, thereference sign CL denotes the tire equatorial plane, and the referencesigns E, E′ denote ground contact edge lines of the pneumatic tire. Alsoto note is that the tread pattern illustrated in FIG. 1 is a patternwith the sides on either side of the tire equatorial plane CL in thetire width direction being asymmetrical.

A tread portion 10 of a pneumatic tire 1 is formed from a rubbermaterial (tread rubber) and is exposed on the outermost side of thepneumatic tire 1 in the tire radial direction. The surface of the treadportion 10 constitutes the contour of the pneumatic tire 1. The surfaceof the tread portion 10 forms a tread surface 12 that is a surface thatcomes into contact with the road surface when a vehicle (notillustrated) on which the pneumatic tire 1 is mounted is driven.

The tread surface 12, as illustrated in FIG. 1, is provided with fourcircumferential grooves 14 a, 14 b, 14 c, 14 d extending in the tirecircumferential direction separated by a predetermined interval in thetire width direction. The circumferential grooves 14 a, 14 c are formedon a vehicle mounting outer side of the tire equatorial plane CL, andthe circumferential grooves 14 b, 14 d are formed on a vehicle mountinginner side. Hereinafter, the circumferential grooves 14 a, 14 b may bereferred to as “center main grooves,” and the circumferential grooves 14c, 14 d may be referred to as “shoulder main grooves.”

Note that in the present embodiment, the circumferential grooves 14 ato14 d are not limited to being grooves that extend in the tirecircumferential direction in a linear manner as illustrated in FIG. 1and may extend in the tire circumferential direction in a wave-like orzigzag-like manner having an amplitude in the tire width direction.

Further, inclined grooves 16 a (16 b, 16 d) are provided at a fixedpitch on the tread surface 12 in the tire circumferential direction.Each inclined groove 16 a extends from the circumferential groove 14 a(14 b, 14 d) toward the vehicle mounting outer side in the samedirection as the tire circumferential direction, and terminates inside aland portion. Note that a chamfered portion 18 a(18 b, 18 d) is formedin each position where the circumferential groove 14 a (14 b, 14 d) andthe inclined groove 16 a (16 b, 16 d) come into contact.

Furthermore, as illustrated in FIG. 1, lug grooves 20 a (20 b), eachextending across the ground contact edge line E (E′), are provided tothe tread surface 12 at a fixed pitch in the tire circumferentialdirection. Note that the lug grooves 20 a provided to the vehiclemounting outer side extend across the shoulder main groove 14 c as well,and a chamfered portion 18 c is formed in each position where theshoulder main groove 14 c and the lug groove 20 a come into contact.

Accordingly, in the present embodiment, five land portions (center landportion X, sub-center land portions Y1, Y2, and shoulder land portionsZ1, Z2) are defined by the grooves 14 a, 14 b, 14 c, 14 d, 16 a, 16 b,16 c, 20 a, 20 b. Note that the center land portion X, the sub-centerland portions Y1, Y2, and the shoulder land portion Z2 are each aso-called rib, and the shoulder land portion Z1 is a block group formedby a large number of blocks.

FIG. 2 is a tire meridian cross-sectional view of the tread portion ofthe pneumatic tire illustrated in FIG. 1. Components in FIG. 2 thatshare reference signs with those in FIG. 1 denote the same member.

As illustrated in FIG. 2, both end points of the center main grooves 14a, 14 b in the tire width direction are taken as A1, A2, A3, A4, andboth end points of the shoulder main grooves 14 c, 14 d in the tirewidth direction are taken as A5, A6, A7, A8.

Then, a curved line including at least two of the four both end pointsA1 to A4 of the two center main grooves 14 a, 14 b in the tire widthdirection is defined as a standard profile line PL0. Examples ofselection of the at least two of four points include a combination ofthe two points A1, A3 near the tire equatorial plane CL, a combinationof the two points A2, A4 away from the tire equatorial plane, and acombination of all four of these points as in the example illustrated inFIG. 1. The standard profile line PL0 may be a circular arc, anelliptical arc, or any other kind of curved line.

When defined as such, in the present embodiment, as illustrated in FIG.2, profile line PL1 of the center land portion X defined by the twocenter main grooves 14 a, 14 b protrudes outward in the tire radialdirection further than the standard profile line PL0.

Next, as illustrated in FIG. 2, on either side of the tire equatorialplane CL in the tire width direction, a curved line including theoutermost point A2 (A4) of the center main groove 14 a (14 b) in thetire width direction and the end points A5, A6 (A7, A8) of the shouldermain groove 14 c (14 d) in the tire width direction is taken as profileline PL2 (PL3). The profile line PL2 (PL3) is a profile line shared bythe sub-center land portion Y1 (Y2) and the shoulder land portion Z1(Z2) defined outward of the center main groove 14 a (14 b) in the tirewidth direction, the shoulder land portion Z1 (Z2) defined even furtheroutward than the sub-center land portion Y1 (Y2).

Further, in the present embodiment, as illustrated in FIG. 2, theprofile line PL2 (PL3) protrudes outward in the tire radial directionfurther than the standard profile line PL0.

Further, in the present embodiment, a pitch count Po of the vehiclemounting outer side region and a pitch count Pi of the vehicle mountinginner side region satisfy the relationship Po<Pi. Here, the pitch countin each vehicle mounting side region refers to the number of lug groovesin the tire circumferential direction disposed in the land portionpositioned on the outermost side in the tire width direction of eachregion. That is, as illustrated in FIG. 1, the pitch count in eachvehicle mounting side region is the number of lug grooves 20 a, 20 binthe tire circumferential direction disposed in each of the shoulder landportions Z1, Z2. Further, the vehicle mounting outer side region is theregion from the tire equatorial plane CL to the ground contact edge lineE of the region illustrated in FIG. 1, and the vehicle mounting innerside region is the region from the tire equatorial plane CL to theground contact edge line E′ of the region illustrated in FIG. 1.

Actions

In the present embodiment, as illustrated in FIG. 2, the profile linePL1, the profile line PL2, and the profile line PL3 protrude outward inthe tire radial direction further than the standard profile line PL0,and the relationship Po<Pi is satisfied as illustrated in FIG. 1. As aresult, the following effects are obtained.

FIGS. 3A and 3B are plan views illustrating ground contact patch formsof pneumatic tires. Note that FIG. 3A illustrates a form of aconventional pneumatic tire, and FIG. 3B illustrates a form of thepneumatic tire of the present embodiment illustrated in FIGS. 1 and 2.In other words, while the tread pattern of FIG. 3A is the same as thetread pattern illustrated in FIG. 1 (in a plan view), the profile linesPL1, PL2, PL3 illustrated in FIG. 2 all match the standard profile linePL0.

In other words, in the conventional pneumatic tire, the profile linesPL1, PL2, PL3 illustrated in FIG. 2 all match the standard profile linePL0. Accordingly, due to the low ground contact pressure of the landportions at the center positions in the tire width direction, both endportions in the tire circumferential direction at approximately thecenter positions deform inward toward the land portions, as illustratedin FIG. 3A. Thus, the peripheral line of the ground contact patch takesan uneven shape (see in particular the dotted areas in FIG. 3A). Theuneven shape of the peripheral line causes a footprint length in theland portions at approximately the center positions in the tire widthdirection to be shortened. This in turn adversely affects contact withthe ground and steering stability performance.

In comparison, in the pneumatic tire of the present embodiment, theprofile lines PL1, PL2, PL3 illustrated in FIG. 2 protrude in the tireradial direction past the standard profile line PL0. Thus, the groundcontact pressure of the land portions at approximately the centerpositions in the tire width direction can be made substantially the sameas the ground contact pressure at both outer positions in the tire widthdirection. Accordingly, it is possible to suppress deformation inwardtoward the land portions in both end portions in the tirecircumferential direction at approximately the center positions. As aresult, as illustrated by the dotted line in FIG. 3B, the boundaries ofthe end portions of the land portions X, Y1, Y2, Z1, Z2 (applicable toboth the leading edge and the trailing edge) in the tire circumferentialdirection are positioned on one smooth curved line, in relation to theground contact surface. This allows for the footprint length of the landportions X, Y1, Y2, Z1, Z2 in the tire width direction to besubstantially uniform compared to the example illustrated in FIG. 3A,thus enhancing contact with the ground (Action 1).

Further, in the present embodiment, there is particular significance tosetting the one profile line PL2 (PL3) ranging across the sub-centerland portion Y1 (Y2) and the shoulder land portion Z1 (Z2), or in otherwords, positioning the outer contour of the sub-center land portion Y1(Y2) and the outer contour of the shoulder land portion Z1 (Z2) on thesame curved line, as illustrated in FIG. 2.

In other words, by setting the one profile line PL2 (PL3) ranging acrossthe sub-center land portion Y1 (Y2) and the shoulder land portion Z1(Z2), the contact with the ground in the tire width direction of thesub-center land portion Y1 (Y2) and the shoulder land portion Z1 (Z2)can be enhanced. Additionally, when the sub-center land portion Y1 (Y2)and the shoulder land portion Z1 (Z2) are considered as a whole, theamount of deformation in the tire width direction of the contact withthe ground can be smoothly transferred amongst these land portions, andin particular, the contact with the ground of the outer shoulder regionsin the tire width direction can be sufficiently enhanced (Action 2).

Furthermore, in the present embodiment, satisfaction of the relationshipPo<Pi makes it possible to comparatively increase the pitch count (thatis, dispose a comparatively large number of lug grooves in the tirecircumferential direction) in the vehicle mounting inner side region,which contributes highly to anti-noise/vibration performancecomparatively large, and thus disperse noise and vibration (Action 3).Further, satisfaction of the Po<Pi relationship makes it possible tocomparatively decrease the pitch count (that is, dispose a comparativelysmall number of lug grooves in the tire circumferential direction) onthe vehicle mounting outer side, which contributes highly to steeringstability performance and the like, and thus increase land portionrigidity (Action 4).

Thus, in the pneumatic tire of the present embodiment, contact with theground in the tire width direction of the land portions is increased(Action 1), contact with the ground between the sub-center land portionand the shoulder land portion is increased (Action 2), and the number oflug grooves in the vehicle mounting outer side region is comparativelydecreased, increasing land portion rigidity (Action 4). According to thepneumatic tire of the present embodiment, Actions 1, 2, and 4 arecombined, making it possible to achieve superior steering stabilityperformance (including both straight-line performance and turningperformance; including, for example, lane changing ease) as well assuperior uneven wear resistance performance.

Further, in the pneumatic tire of the present embodiment, the number oflug grooves in the vehicle mounting inner side region is comparativelyincreased, making it possible to disperse the noise and vibration(Action 3) and thus achieve superior anti-noise/vibration performance.

Thus, according to the pneumatic tire of the present embodiment, withthe combined Actions 1 to 4 above, the steering stability performance,anti-noise/vibration performance, and uneven wear resistance performancecan be achieved in a well-balanced manner.

Although it is not illustrated in the drawings, the pneumatic tireaccording to the present embodiment described above has a meridiancross-section shape similar to that of a conventional pneumatic tire.Here, the meridian cross-section shape of the pneumatic tire refers tothe cross-sectional shape of the pneumatic tire on a plane normal to thetire equatorial plane. As seen in the tire meridian cross-section, thepneumatic tire according to the present embodiment includes beadportions, sidewall portions, shoulder portions, and the tread portionfrom inside to outside in the tire radial direction. As seen, forexample, in the tire meridian cross-section, the pneumatic tire isprovided with a carcass layer that extends from the tread portion to thebead portions on both sides and is wound around a pair of bead cores,and a belt layer and a belt reinforcing layer upon the carcass layers inthat order outward in the tire radial direction.

The pneumatic tire according to the present embodiment can be obtainedvia ordinary manufacturing steps; i.e., a tire material mixing step, atire material machining step, a green tire molding step, a vulcanizationstep, a post-vulcanization inspection step, and the like. In particular,when manufacturing the pneumatic tire according to the presentembodiment, for example, recesses and protrusions corresponding to thegrooves and land portions formed in the tread portion illustrated inFIGS. 1 and 2 are formed on the inner wall of the vulcanization mold,which is used for vulcanization.

Note that in the pneumatic tire of the present embodiment, the followingmethod is used to determine, in particular, the profile lines PL1, PL2,PL3 illustrated in FIG. 2.

In other words, first, the shape of the standard profile line PL0 isdetermined. For example, when the standard profile line PL0 is acircular arc, the radius of curvature is determined. For the radius ofcurvature, it is important to set various values according to the tiresize. In the present embodiment, the radius of curvature is a dimensionfrom 5 to 20 times that of the cross-sectional height of the tire.

Then, the circular arc PL0 with a radius of curvature R0 including atleast two of the four both end points A1, A2, A3, A4 of the two centermain grooves 14 a, 14 b in the tire width direction (point A1 and pointA3, for example) and having a center position on the tire equatorialplane CL is determined.

Next, the circular arc PL1 with a radius of curvature R1 including theinner points A1, A3 of the two center main grooves 14 a, 14 b in thetire width direction is determined, the radius of curvature R1 beingless than the radius of curvature R0 of the circular arc PL0(0.3≤R1/R0≤0.4).

Lastly, the circular arc PL2 (PL3) with a radius of curvature R2 (R3)including the point A2 (A4) on the outer side of the two center maingrooves 14 a (14 b) in the tire width direction is determined, theradius of curvature R2 (R3) being less than the radius of curvature R0of the circular arc PL0 (0.75≤R2 (R3)/R0≤0.95). The circular arc PL2(PL3) extends from the point A2 (A4) beyond the ground contact edge lineE (E′) outward in the tire width direction and intersects the circulararc PL0 at point P (P′).

Note that the circular arc PL1 and the circular arc PL2 (PL3) intersectin the tire width direction region of the circumferential groove 14 a(14 b) near the tire equatorial plane CL. Additionally, the point P (P′)is positioned further outward in the tire width direction from theground contact edge line E (E′) by a dimension from 3% to 5% the tireground contact width.

When the standard profile line PL0 is a circular arc and the radius ofcurvature of the circular arc is 5 times or greater than thecross-sectional height of the tire, the standard profile line PL0 itselfcan be prevented from protruding excessively in the tire radialdirection. Thus, the radius of curvature of the profile lines PL1, PL2,PL3 that protrude outward in the tire radial direction further than thestandard profile line PL0 need not be set excessively low to achievesufficient enhancement of the contact with the ground of the landportions. When the radius of curvature described above is 20 times orless than the cross-sectional height of the tire, the standard profileline PL0 itself can protrude sufficiently in the tire radial direction.Thus, the radius of curvature of the profile lines PL1, PL2, PL3 thatprotrude outward in the tire radial direction further than the standardprofile line PL0 can be set sufficiently low to achieve sufficientenhancement of the contact with the ground of the land portions.

After the shape of the standard profile line PL0 (radius of curvaturewhen a circular arc) is determined as such, at least two of both endpoints A1 to A4 of the center main grooves 14 a, 14 b in the tire widthdirection on the standard profile line PL0 are determined. Then, asillustrated in FIG. 2, the profile line PL1 of the center land portion Xis determined together with the profile line PL2 (PL3) ranging acrossthe sub-center land portion Y1 (Y2) and the shoulder land portion Z1(Z2).

Additional Embodiments

Next, Additional Embodiments 1 to 3 are described that can optionally beimplemented on the Basic Embodiment of the pneumatic tire according tothe present technology as described above.

Additional Embodiment 1

In the Basic Embodiment, the profile line PL1 of the center land portionX illustrated in FIG. 2 preferably has a maximum protruding amountoutward in the tire radial direction with respect to the standardprofile line PL0 of from 0.2 to 0.5 mm (Additional Embodiment 1).

FIG. 4 is an enlarged view of the circled area B of FIG. 2. In thepresent embodiment, as illustrated in FIG. 4, the profile line PL1 ofthe center land portion X has a maximum protruding amount S1 outward inthe tire radial direction with respect to the standard profile line PL0.The maximum protruding amount S1 is the maximum dimension in the tireradial direction from the standard profile line PL0 to the profile linePL1.

When the maximum protruding amount S1 is 0.2 mm or greater, in thecenter land portion X, the ground contact pressure at approximately thecenter position in the tire width direction can be made even closer tothe ground contact pressure at both outer positions in the tire widthdirection. Accordingly, gripping force to the road surface can beenhanced, and in particular, steering characteristics when travelingstraight are enhanced and straight-line performance (steering stabilityperformance) can be further enhanced.

Additionally, when the maximum protruding amount S1 is 0.5 mm or less,in the center land portion X, the protruding amount in the tire radialdirection at approximately the center position in the tire widthdirection can be suppressed. Thus, the amount of wear at approximatelythe center position is not excessive compared to the amount of wear atother positions, and uneven wear resistance performance can be furtherenhanced.

Note that when the maximum protruding amount S1 is from 0.3 to 0.4 mm,the effects described above can be obtained at an even higher level.

Additional Embodiment 2

In Basic Embodiment and Basic Embodiment with Additional Embodiment 1applied, as illustrated in FIG. 2, the profile line PL2 (PL3) of thesub-center land portion Y1 (Y2) and the shoulder land portion Z1 (Z2)preferably has a maximum protruding amount S2 (S3) outward in the tireradial direction with respect to the standard profile line PL0 of from0.6 to 2.0 mm; additionally, the profile line PL2 on the vehiclemounting inner side and the profile line PL3 on the vehicle mountingouter side preferably have different maximum protruding amounts S2 (S3)(Additional Embodiment 2).

When the maximum protruding amount S2 (S3) is 0.6 mm or greater, in thesub-center land portion Y1 (Y2) and the shoulder land portion Z1 (Z2),the ground contact pressure at approximately the center position in thetire width direction can be made even closer to the ground contactpressure at both outer positions in the tire width direction.Accordingly, gripping force to the road surface can be enhanced, and inparticular, steering characteristics when traveling straight areenhanced and straight-line performance (steering stability performance)can be further enhanced.

Additionally, when the maximum protruding amount S2 (S3) is 2.0 mm orless, in the sub-center land portion Y1 (Y2) and the shoulder landportion Z1 (Z2), the protruding amount in the tire radial direction atthe center position in the tire width direction can be suppressed. Thus,the amount of wear at approximately the center position is not excessivecompared to the amount of wear at other positions, and uneven wearresistance performance can be further enhanced.

Note that when the maximum protruding amount S2 (S3) is from 0.9 to 1.7mm, the effects described above can be obtained at an even higher level.

Additionally, in the present embodiment, the maximum protruding amountsS2 (S3) of the profile line PL2 on the vehicle mounting inner side andthe profile line PL3 on the vehicle mounting outer side are made todiffer. That is, in the present embodiment, for example, the degree ofprotrusion of the land portions on the vehicle mounting outer sidehaving a significant amount of wear during cornering (the sub-centerland portion Y1 and the shoulder land portion Z1) can be intentionallyset comparatively low to suppress the amount of wear. In such a case,the tire from the start to end of its service life does not differgreatly in terms of the amount of wear at the land portions on thevehicle mounting outer side and inner side, thus uneven wear resistanceperformance can be further enhanced.

Additional Embodiment 3

In Basic Embodiment and Basic Embodiment with at least one of AdditionalEmbodiments 1 and 2 applied, preferably the pitch count Po on thevehicle mounting outer side and the pitch count Pi on the vehiclemounting inner side satisfy the relationships 50≤Pi≤100 and 30≤Po≤80(Additional Embodiment 3).

Setting the pitch count Pi on the vehicle mounting inner side to 50 orgreater makes it possible to sufficiently dispose the lug grooves in thevehicle mounting inner side region, which readily impactsanti-noise/vibration performance in particular, further disperse thenoise and vibration, and thus further increase anti-noise/vibrationperformance. Further, setting the pitch count Pi on the vehicle mountinginner side to 100 or less makes it possible to further ensure landportion rigidity, and thus further increase steering stabilityperformance without excessively disposing lug grooves in the vehiclemounting inner side region.

On the other hand, setting the pitch count Po on the vehicle mountingouter side to 30 or greater makes it possible to sufficiently disposethe lug grooves in the vehicle mounting outer side region as well,further disperse the noise and vibration, and thus further increaseanti-noise/vibration performance. Further, setting the pitch count Po onthe vehicle mounting outer side to 80 or less makes it possible tofurther ensure land portion rigidity, and thus further increase steeringstability performance without excessively disposing lug grooves in thevehicle mounting outer side region as well.

Note that when the pitch count Pi on the vehicle mounting inner side andthe pitch count Po on the vehicle mounting outer side indicated aboveare respectively set so that 60≤Pi≤80 and 50≤Po≤70, each of the effectsdescribed above can be exhibited at a higher level.

EXAMPLES

Pneumatic tires of Examples 1 to 6 were manufactured with a tire size of235/40ZR18 (95Y) and included a tread pattern similar to the treadpattern illustrated in FIG. 1 and the profile lines PL1, PL2, PL3 of thetread surface illustrated in FIG. 2 (FIG. 4). Note that the profilelines of the tread surface of the pneumatic tires of Examples 1 to 6 haddetails with the conditions indicated in Table 1 below.

Additionally, pneumatic tires of a conventional example weremanufactured with a tire size of 235/40ZR18 (95Y) and had the sameconfiguration as the pneumatic tires of Example 1 except that theprofile lines PL1, PL2, PL3 of the tread surface illustrated in FIG. 2coincided with the standard profile line PL0.

The test tires thus manufactured for Examples 1 to 6 and theconventional example were assembled to 18×8.5J rims, set to an airpressure of 230 kPa, and fitted to a sedan type passenger vehicle withan engine displacement of 2000 cc. Evaluation was carried out onsteering stability performance 1 (straight-line performance), steeringstability performance 2 (turning performance), anti-noise/vibrationperformance, and uneven wear resistance performance.

Steering Stability Performance 1 (Straight-line Performance)

On a dry road surface, performance evaluation was carried out on vehiclestability when traveling straight. Then, the results were expressed asindex values for evaluation with the result for the conventional examplebeing defined as the reference (100). Higher index values indicatebetter steering stability performance 1 (straight-line performance).

Steering Stability Performance 2 (Turning Performance)

On a dry road surface, performance evaluation was carried out on vehiclestability when turning. Then, the results were expressed as index valuesfor evaluation with the result for the conventional example beingdefined as the reference (100).

In the evaluation, higher index values indicate better steeringstability performance 2 (turning performance).

Anti-Noise/Vibration Performance

Using the above test vehicle, pass-by noise was measured on the basis ofthe acceleration noise test method defined in the ISO 362 pass-by noiseperformance standard. Then, the results were expressed as index valuesfor evaluation with the result for the conventional example beingdefined as the reference (100). In the evaluation, higher index valuesindicate better anti-noise/vibration performance.

Uneven Wear Resistance Performance

After traveling for 1000 km on a dry road surface, the amount of wear ofthe center land portion X and the shoulder land portion Z1 (Z2) weremeasured. For the shoulder land portions, the amount of wear on bothsides in the tire width direction were averaged, then an amount of wearratio between the center land portion and the shoulder land portion wascalculated. Then, index evaluation was performed on the basis of themeasured results using the conventional example as a reference (100). Inthe evaluation, higher index values indicate better uneven wearresistance performance.

The results are shown in Table 1-1 and Table 1-2.

TABLE 1-1 Conventional example Example 1 Example 2 Example 3 Maximumprotruding amount S1 0 0.1 0.35 0.35 (mm) illustrated in FIG. 4 Maximumprotruding amount S2 0 0.5 0.5 1.2 (mm) illustrated in FIG. 2 Maximumprotruding amount S3 0 0.5 0.5 1.4 (mm) illustrated in FIG. 2Relationship between pitch count Po < Pi Po < Pi Po < Pi Po < Pi Po ofvehicle mounting outer side region and pitch count Pi of vehiclemounting inner side region Pitch count Po 25 25 25 25 Pitch count Pi 4040 40 40 Pitch variation presence/absence Absent Absent Absent Absent(Corresponding figure) (FIG. 1) (FIG. 1) (FIG. 1) (FIG. 1) Steeringstability performance 1 100 101 105 105 (straight-line performance)Steering stability performance 2 100 103 103 110 (turning performance)Anti-noise/vibration performance 100 100 100 100 Uneven wear resistance100 100 103 105 performance

TABLE 1-2 Exam- ple 4 Example 5 Example 6 Maximum protruding amount S1(mm) 0.35 0.35 0.35 illustrated in FIG. 4 Maximum protruding amount S2(mm) 1.2 1.2 1.2 illustrated in FIG. 2 Maximum protruding amount S3 (mm)1.4 1.4 1.4 illustrated in FIG. 2 Relationship between pitch count Po Po< Pi Po < Pi Po < Pi of vehicle mounting outer side region and pitchcount Pi of vehicle mounting inner side region Pitch count Po 35 25 35Pitch count Pi 40 60 60 Pitch variation presence/absence Absent AbsentAbsent (Corresponding figure) (FIG. 1) (FIG. 1) (FIG. 1) Steeringstability performance 1 105 105 105 (straight-line performance) Steeringstability performance 2 110 113 110 (turning performance)Anti-noise/vibration performance 95 100 103 Uneven wear resistanceperformance 105 105 105

According to Table 1-1 and Table 1-2, the pneumatic tires of Examples 1to 6 affiliated with the technical scope of the present technology(enhanced profile line of the land portions defined by the treadportion, and enhanced pitch count of the tread portion) were each foundto have steering stability performances 1, 2, anti-noise/vibrationperformance, and uneven wear resistance performance enhanced in awell-balanced manner compared to the pneumatic tire of the conventionalexample not affiliated with the technical scope of the presenttechnology.

The invention claimed is:
 1. A pneumatic tire, comprising on each ofboth sides of a tire equatorial plane in a tire width direction, onecenter main groove extending in a tire circumferential direction, oneshoulder main groove extending in the tire circumferential directionoutward from the center main groove in the tire width direction, andfive land portions extending in the tire circumferential direction, theland portions being defined by the four main grooves; in a tire meridiancross-section, a curved line including at least two of four both endpoints of the two center main grooves in the tire width direction beingdefined as a standard profile line; a profile line of a center landportion defined by the two center main grooves protruding outward in atire radial direction further than the standard profile line; profilelines of sub-center land portions and shoulder land portions definedoutward of the two center main grooves in the tire width directionprotruding outward in the tire radial direction further than thestandard profile line, the shoulder land portions being defined furtheroutward than the sub-center land portions, and the profile lines of thesub-center land portions and the shoulder land portions each includingan outermost point of the corresponding center main groove in the tirewidth direction and both end points of the corresponding shoulder maingroove in the tire width direction, and being present on either side ofthe tire equatorial plane in the tire width direction; and a pitch countPo of a vehicle mounting outer side region and a pitch count Pi of avehicle mounting inner side region satisfying the relationship Po<Pi;wherein one of the center main grooves is positioned on a vehiclemounting outer side and the other of the center main grooves ispositioned on a vehicle mounting inner side; the one shoulder maingroove on either side of the tire equatorial plane in the tire widthdirection includes a narrower width shoulder main groove positioned onthe vehicle mounting outer side, the narrower width shoulder main groovehaving a narrower width than a wider width shoulder main groovepositioned on the vehicle mounting inner side; the sub-center landportions are ribs; a plurality of lateral grooves that is disposed inthe center land portion only communicates with the center main groovepositioned in the vehicle mounting inner side and does not communicatewith the tire equatorial plane; and a maximum protruding amount of theprofile line on the vehicle mounting inner side is greater than amaximum protruding amount of the profile line on the vehicle mountingouter side.
 2. The pneumatic tire according to claim 1, wherein theprofile line of the center land portion has a maximum protruding amountoutward in the tire radial direction with respect to the standardprofile line of from 0.2 to 0.5 mm.
 3. The pneumatic tire according toclaim 2, wherein the profile lines of the sub-center land portions andthe shoulder land portions have a maximum protruding amount outward inthe tire radial direction with respect to the standard profile line offrom 0.6 to 2.0 mm, the maximum protruding amount of the profile line onthe vehicle mounting inner side and the maximum protruding amount of theprofile line on the vehicle mounting outer side being different.
 4. Thepneumatic tire according to claim 3, wherein the pitch count Po on thevehicle mounting outer side and the pitch count Pi on the vehiclemounting inner side satisfy the relationships 50≤Pi≤100 and 30≤Po≤80. 5.The pneumatic tire according to claim 1, wherein the profile lines ofthe sub-center land portions and the shoulder land portions have amaximum protruding amount outward in the tire radial direction withrespect to the standard profile line of from 0.6 to 2.0 mm, the maximumprotruding amount of the profile line on the vehicle mounting inner sideand the maximum protruding amount of the profile line on the vehiclemounting outer side being different.
 6. The pneumatic tire according toclaim 1, wherein the pitch count Po on the vehicle mounting outer sideand the pitch count Pi on the vehicle mounting inner side satisfy therelationships 50≤Pi≤100 and 30≤Po≤80.
 7. The pneumatic tire according toclaim 1, wherein the center main groove positioned in the vehiclemounting inner side is narrower than the center main groove positionedin the vehicle mounting outer side.
 8. The pneumatic tire according toclaim 1, wherein the four main grooves are substantially linear.